1. Field of the Invention
This invention relates to a method and apparatus for forming a workpiece by pressing the workpiece in a mold and passing a hot gas through the workpiece and more particularly to forming an automotive headliner by shaping the headliner between dies and then passing a hot gas through the dies and the headliner.
2. Description of the Prior Art
Automotive headliners, fabric with a foam backing, fibers mixed with adhesive materials and other similar articles have been formed by placing the material from which the articles are made in a mold cavity of the desired shape and then passing super heated steam through the articles to activate an adhesive or to soften thermally softenable materials and cause the materials from which the articles are made to adhere to each other. Such articles have also been formed by passing a heated gas through the article rather than super heated steam.
Super heated steam can in some cases result in condensation of water on the surface of an article that has been formed. The water can discolor or stain the article and may change the surface texture. Another problem that is frequently encountered is delamination of the article. Delamination may be caused by water or it can be caused by an expansion of the gas inside the article due to pressure differentials between the gas inside the article and the pressure on the outside surface of the article. A further problem is energy loss. Superheated steam is released during molding and is very difficult to recapture. The energy required to heat the steam is lost with the steam.
A number of the article forming processes employing super heated steam, that are currently used, treat the article with a cooling gas after the steam treatment to reduce the temperature of a workpiece and rigidify thermoplastic material if used. The cooling gas treatment forces water out and reduces the problems mentioned above. However, the cooling gas treatment increases cost and increases the time required to form each article even when the forming operation is continuous.
The article forming systems employing heated gas that have been used tend to be slow due to the time required to heat the gas. It takes time to heat gasses. It may also be difficult to control the temperature of the gasses during heating. Depending on the materials used to make the article being formed, temperature control may be critical.
Energy is required to heat steam and to heat gas. The systems currently used to form an article in a mold cavity by passing steam or hot gas through the article all require substantial amounts of energy. These systems do not recapture gas, steam or the energy required to heat the steam or gas. Increases in energy costs increase the cost of producing articles by processes that use substantial amounts of energy.